I have an s410 carbine and have noticed that after 40y the pellets are drifting to the left, l have used several types,sizes,&makes of pellets with differing results as expected, but the good ones with tight grouping etc are only good to 40y then 45y quarter mile dot left 50y half mile dot left this is where I stop as my scope and eyes are at max ability. Anyone got any ideas what is happening or is this normal, does parallax effect left/ right poi ?

sounds like you have cross over with your scope. question for you. at your zero spot on beyond to the left, does it shoot slightly to the right at distances less than your zero. you can try putting the mounts the other way around. hope you are using a good set of mounts as this is an item over looked by some yet very important. keep us informed.